The human eye functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of a crystalline lens onto a retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and the lens. When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. An accepted treatment for this condition is surgical removal of the lens and replacement of the lens function by an artificial intraocular lens (IOL).
In the United States, the majority of cataractous lenses are removed by a surgical technique called phacoemulsification. A typical surgical handpiece used for phacoemulsification procedures includes of an ultrasonically driven cutting needle surrounded by an irrigating sleeve and is attached to an electronic control surgical system. The handpiece is attached to the control surgical system by an electric cable and flexible conduit. Through the electric cable, the surgical system varies the power level transmitted by the handpiece to the attached cutting needle. The flexible conduit supplies irrigation fluid to the surgical site and draws aspiration fluid from the eye through the handpiece assembly.
During the phacoemulsification procedure, the tip of the cutting needle and the end of the irrigation sleeve are inserted into the anterior segment of the eye through a small incision in the outer tissue of the eye. The surgeon brings the tip of the cutting needle into contact with the lens of the eye, and the vibrating tip fragments the lens. The resulting fragments are aspirated out of the eye through the interior bore of the cutting needle and transported to a drain reservoir.
A common complication during the phacoemulsification process arises from a blockage or occlusion of the aspirating needle. As the irrigation fluid and emulsified tissue are aspirated away from the interior of the eye through the hollow cutting needle, fragments of tissue that are larger than the diameter of the needle's bore may become clogged in the needle's tip. While the tip is clogged, vacuum pressure builds up within the aspiration conduit, including lumen of the cutting needle. Once the occlusion is cleared, a surge of fluid is removed from the eye due to a vacuum formed within the aspiration conduit. The resulting drop in pressure in the anterior chamber in the eye when the occlusion is removed is known as post-occlusion surge. This post-occlusion surge can, in some cases, cause a relatively large quantity of fluid and tissue to be aspirated out of the eye too quickly, potentially causing the eye to collapse and/or causing the lens capsule to be torn.